1. Field of the Invention
The present invention relates to bandwidth control techniques in an ATM (asynchronous transfer mode) network, and more particularly to control method and system for controlling the bandwidth of a link between communication devices in the ATM network.
2. Description of the Related Art
A Broadband-ISDN (Integrated Services Digital Network) based on an ATM technology extends the digital transmission capabilities defined by ISDN to allow high-speed voice, data, and moving picture for multimedia transmissions on the same lines with reliability.
Information exchanges in the ATM network are carried out either on a permanent virtual channel (PVC) connection with fixed communication parties or on a switched virtual channel (SVC) connection in which communication parties can be selected.
The PVC connection is a connection established when a subscriber declares in advance a communication bandwidth for carrying out data communications at the time of making a contract with an ATM network provider.
On the other hand, the SVC connection is a connection established by the following steps. At first, when a subscriber requires a communication line for carrying out data communication, the subscriber sets a required communication bandwidth to a SETUP message based on a user-network interface (UNI) signaling procedure and transmits this SETUP message to the ATM network. This causes a line connection negotiation with the ATM network to establish the connection. The UNI signaling procedure is a procedure as prescribed in the ATM Forum Technical Committee User-Network Interface (UNI) Specification Version 3.1, the ATM Forum Technical Committee ATM UNI signaling Specification Version 4.0, ITU-T Recommendation Q.2931, and ITU-T Recommendation Q.2971.
In the ATM public network, convenience of users and flexibility of the ATM network are being improved by carrying out establishment and release of SVC connections according to the UNI signaling procedure between the ATM switches. The bandwidth control system is being investigated as a means for further improving the flexibility of the ATM network and for providing effective utilization of data communication bandwidths by restricting redundancies within the ATM public network.
One example of a conventional bandwidth control system is a system for carrying out bandwidth control in the process of establishing a SVC connection according to the UNI signaling procedure. According to this conventional system, an ATM switch includes a signaling controller for controlling the processing of the UNI signaling procedure, and a bandwidth controller for controlling the communication bandwidths of an ATM cell transmission line and an ATM cell reception line using a single bandwidth management table.
When the signaling controller receives a SETUP message (a setup request for an SVC connection) according to the UNI signaling procedure from a subscriber ATM terminal or an ATM subscriber transmission apparatus through a UNI signaling channel, the signaling controller outputs this SETUP message to the bandwidth controller. The bandwidth controller obtains a bandwidth value declared to the ATM public network from the received SETUP message, and decides whether or not it is possible to establish the requested bandwidth by referring to the bandwidth management table. In this decision, the bandwidth controller decides both a data transmission line and a data reception line together.
In other words, bandwidth information of both a transmitter side unused bandwidth and receiver side unused bandwidth is set in the bandwidth management table. The bandwidth controller compares the requested bandwidth value obtained from the SETUP message with the unused bandwidths for each of the transmitter side unused bandwidth and the receiver side unused bandwidth. As a result, if it has been confirmed in both bandwidths that the requested bandwidth value is smaller than the unused bandwidth value, the bandwidth controller informs the signaling controller that the request for an establishment of an SVC connection is possible. Then, the signaling controller starts the processing of the UNI signaling procedure such as a transmission of the SETUP message and the like.
On the other hand, if it has been confirmed in both bandwidths that the requested bandwidth value is greater than the unused bandwidth value, the bandwidth controller informs the signaling controller that the request for an establishment of an SVC connection is not possible. Then, the signaling controller stops the processing of the UNI signaling procedure.
According to another conventional bandwidth control, when it is necessary to establish a new SVC connection in an ATM cell transmission line and an ATM cell reception line, the signaling controller establishes the SVC connection according to the UNI signaling procedure. This SVC connection becomes the data channel for data communications. Thereafter, the bandwidth controller controls the bandwidth by transmitting and receiving bandwidth control information to and from the opposite party device of the transmission line through this data channel.
There has been still another conventional system for carrying out bandwidth control according to an originally defined procedure. A CLAD apparatus of ATM network is disclosed in Japanese Patent Application Laid-open Publication No. 8-204723. In the CLAD apparatus, there is disclosed a bandwidth control system for achieving the bandwidth control of the ATM public network by defining an own format for the bandwidth control in OAM (operation and maintenance) cell which are originally designed for carrying out fault management or performance management and transmitting and receiving bandwidth control information by transmitting and receiving the OAM cells through the data channel.
Further, an ATM communication terminal apparatus is disclosed in Japanese Patent Application Laid-open Publication No. 7-143128. According to the ATM communication terminal apparatus, there is disclosed a bandwidth control system for achieving the bandwidth control of the ATM public network by defining an own cell format for the bandwidth control and transmitting and receiving the cells through the data channel.
According to the conventional bandwidth control system where both the communication bandwidth of the ATM cell transmission line and the communication bandwidth of the ATM cell reception line are managed together in the single bandwidth management table, it becomes necessary to install tables for managing mutually different communication bandwidths for ATM cell transmission and reception lines of different bandwidths in the case where the communication bandwidths asymmetrical in upstream and downstream directions are to be controlled.
Particularly, in the case where an ATM subscriber transmission apparatus accommodating a large number of subscriber ATM terminals carries out a bandwidth control of the ATM subscriber line, the above-described new installation of bandwidth management tables leads to an increase in the memory capacity provided in the ATM subscriber transmission apparatus, resulting in cost increase. This is against the requirement that the ATM subscriber network should be structured at low cost, and thus this must be avoided.
Further, in the case where an SVC connection cannot be established if the requested bandwidth value is larger than the unused bandwidth value, however, there is also such a possibility that the ratio of the unused bandwidth value to the requested bandwidth value is relatively high, for example, 0.95, although the requested bandwidth value is larger than the unused bandwidth value. If the unused bandwidth ratio is 0.95, for example, it must be possible to carry out sufficient data communications if an SVC connection is established by using the unused bandwidth value of the bandwidth management table with this 95% set as a communication bandwidth guarantee factor.
Since it is not possible to carry out flexible bandwidth control in the conventional bandwidth control system as described above, there is a possibility that this conventional system increases a refusal rate of a request for establishing an SVC connection and further generates a surplus of unused communication bandwidth.
Furthermore, according to the bandwidth control system disclosed in the above publications, bandwidth control is carried out based on an own procedure that bandwidth information is set in OAM cells and ATM cells after establishing a data channel. If an ATM network such as an ATM public network or an ATM subscriber network is constructed by including apparatuses having different bandwidth control systems, each apparatus transmits cells for executing the bandwidth control of an ATM network. However, there is a possibility that one apparatus cannot understand cells transmitted from the other apparatus, thus failing in achieving a targeted effective bandwidth control.
It is an object of the present invention to provide a bandwidth control method and system capable of achieving a flexible control and effective utilization of a communication bandwidth for an ATM network.
It is another object of the present invention to provide a bandwidth control method and system capable of achieving mutual connections of communication devices without increasing the cost thereof.
According to the present invention, in a communication device including a transceiver for transmitting and receiving ATM cells to and from another communication device through a link, there is provided a transmission bandwidth controller for making a decision as to whether it is possible to allocate a requested transmission bandwidth for requested data transmission through the link by referring to a bandwidth management table. A signaling controller controls the processing of a UNI (User-Network Interface) signaling procedure based on a result of the decision of transmission bandwidth allocation.
The transmission bandwidth controller preferably holds a communication bandwidth guarantee factor. If the requested transmission bandwidth is greater than an available transmission bandwidth in the link, the transmission bandwidth controller compares an available bandwidth ratio of the available transmission bandwidth to the requested transmission bandwidth with the communication bandwidth guarantee factor to make a decision as to whether it is possible to allocate a practicable transmission bandwidth for the data transmission.
Further, if the available bandwidth ratio is greater than the communication bandwidth guarantee factor, then the transmission bandwidth controller reduces the requested transmission bandwidth into a practicable transmission bandwidth and determines that it is possible to allocate the practicable transmission bandwidth. Thereafter, the signaling controller produces a SETUP message for making a request for establishing the virtual channel having the practicable transmission bandwidth in the link, and then starts the UNI signaling procedure. If the available bandwidth ratio is smaller than the communication bandwidth guarantee factor, then the transmission bandwidth controller determines that it is not possible to allocate a practicable transmission bandwidth and the signaling controller stops the UNI signaling procedure.
According to another aspect of the present invention, in a bandwidth control system for a link between communication devices, each comprising: a transceiver for transmitting and receiving ATM cells to and from another communication device through the link; a bandwidth management table containing a call reference, an allocated transmission bandwidth, a currently-used transmission bandwidth, and an unused transmission bandwidth; a bandwidth controller for controlling a bandwidth for only data transmission using the bandwidth management table and for making a decision as to whether it is possible to allocate a requested transmission bandwidth for requested data transmission through the link by referring to the bandwidth management table; and a signaling controller for controlling a UNI (User-Network Interface,) signaling procedure based on a result of the decision of transmission bandwidth allocation.